The use of lithographic technology in transferring patterns from masks to semiconductor substrates in the fabrication of semiconductor devices, such as integrated circuits has been highly developed and widely used. Photomasks, such as those employed in semiconductor device fabrication, are used with a wide variety of radiation sources, both visible and ultraviolet, as well as x-rays and electron beams. An example of an electron beam system is given in Broers et al. U.S. Pat. No. 3,876,883. Other systems employing light as a radiation source are found in U.S. Pat. Nos. 3,152,938; 3,458,370; 3,712,816; and 3,758,346.
A typical mask comprises a transparent substrate, such as glass, quartz and the like, on which is coated a chromium pattern complementary to the pattern desired to be transferred to a substrate. Such mask patterns can also be formed of other compatible compositions such as chrome oxide, iron oxide, nickel and the like. These materials, as well as chromium can be prepared on a transparent substrate by conventional vacuum evaporation, sputtering techniques. However, since the reflectance of a chromium film is very high (about 40 to 60% ) the resolution of a circuit pattern formed by use of the chromium mask is degraded due to multiple reflections between the surfaces of the mask and a semiconductor wafer during exposure. To overcome these problems, as so-called surface reflection-free chromium mask has been proposed, in which a chromium oxide film (of about 250 .ANG. thickness and with anti-reflection properties) is formed over the chromium masking film. Such approaches are described in U.S. Pat. Nos. 4,139,443 and 4,178,403.
A modification of these approaches is described by W. J. Stetson in "Multilayer Antireflective Absorption Mask", p.1319 of the October 1975 issue of the IBM Technical Disclosure Bulletin, v.18, n.5. In this approach a transparent glass substrate is initially coated with a layer of Cr.sub.2 O.sub.3 by any conventional method (such as sputtering in an argon-nitrogen-oxygen ambient under reduced pressure) followed by an overcoating of a normal chrome layer formed by well known techniques such as vacuum deposition, sputtering and the like.
Other methods for forming a chrome oxide coating include vapor deposition, oxidation of chrome coatings deposited as described above.
Also, a glass will typically become statically charged during handling, with even the smallest static charge attracting dust and lint particles to the glass surface. In the case of chrome plated glass photomasks, such particles, by abrasion and optical effects, will result in shorter service life and image degradation resulting in lowered process yields.
For additional background, attention is directed to U.S. Pat. No. 3,877,810 wherein the fabrication of a cobalt mask is described. This mask is formed by coating a glass plate or substrate with a conductive adhesion promoter for cobalt, as for example, stannic oxide, or InO.sub.2 doped with SnO.sub.2. However, retention of such a tin coating on the Mask can induce transmittance loss, is subject to degradation or removal with plasma and acid processing, as well as removal on stripping of the masking (e.g. chrome) for reprocessing to form new masks.